STAPHYLOCOCCUS - MICROBIOLOGY

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 STAPHYLOCOCCUS🦠

  • Staphylococci are gram positive cocci arranged in grape like cluster
  • The pathogenic medically important species:
1)Staphylococcus aureus 
2) Staphylococcus epidermidis
3) Staphylococcus saprophyticans

Morphology :

  • Non motile
  • Non sporing
  • 1 micro meter in diameter

Culture : 

  • They grow on ordinary culture media at 37 degree Celsius temperature
  • They are aerobe and facultative anaerobe

1) Nutrient agar :

  •  After 24 hours incubation,colonies : circular,smooth,convex

2) Blood agar:

  • Colonies similar to nutrient agar

3)Macconkey agar:

  • Colonies : small and pink

4)MANNITOL SALT AGAR: 

  • This is both selective and an indicator medium 
  • Colonies : yellow colored 

Toxin

1) Staphylococci produce 4 antigenically distinct type of exotoxin

Alpha lysin:

  • Lytic to rabbit erythrocyte ,less active against sheep or human red cell
  • It is cytotoxic ,leucocidal and dermonecrotic

Beta lysin:

  • Lytic to sheep cell but not to human or rabbit erythrocyte
  • Hot -cold phenomenon : lysis is initiated at 37 degree Celsius ,evident only on cold temperature

Gama lysin and delta lysin :

  •  Lytic to human ,sheep and rabbit red blood cell

Panton-valentine leucocidin

  • Its composed of two component slow and fast
  • Components damage polymorphonuclear leukocyte and macro phage

Enterotoxin:

  • The toxin is responsible for staphylococcal food poisoning
  • Nine antigenically distinct type of enterotoxin 9 (A,B,C1,C2,C3,D,E,H,I)
  • Enterotoxin resistant to gut enzyme

Toxic shock syndrome ( TSST)

  • Most TSST producing strain belong to bacteriophage type 1


ENZYME:

  • Staphylococcus aureus produce number of enzyme ,coagulase,phosphatase and deoxyribonuclease.
  • Coagulase is secreted free into culture medium,heat labile
  • Coagulase convert fibrinogen into fibrin
  • Test for coagulase is done on slide and tube 
  • Its done to differentiate pathogenic strain from non-pathogenic strain.

LABORATORY DIAGNOSIS:

1)SPECIMEN:

  • These are collected according to nature of lesion,pus ,sputum,blood and urine

2) Collection and transport 

  • Collected in sterile container and transported to lab

3) Culture:

  • Specimen inoculated on blood agar ,peptone water

4) Biochemical reaction:

  1. Catalase test: test distinguish staphylococcus from streptococcus ,staph - positive,strep-negative
  2. Coagulase test:positive in staphylococcus 

AIM OF THIS POST:

Hi stencildent mates,hope you all are doing fine ,the topic covered in this post are small introduction to staphylococcus ,morphology,culture,toxin,enzyme,and finally the laboratory diagnosis of staphylococcus is been discussed hope you all found this post useful,if it helped you do let me know in the comment section below .
contact : stencildent@gmail.com 
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                                   THANK YOU 🙏🏻 


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